Abstract
Different 2D zeolites, namely lamellar ZSM-5 (L-ZSM-5), the corresponding silica pillared ZSM-5 (PI-ZSM-5) and an MCM-22 sample, were investigated as nickel phosphide supports and evaluated as catalysts for guaiacol hydrodeoxygenation (HDO). Characterization confirmed that all loaded materials preserved a high crystallinity degree with formation of the Ni2P phase.
The incorporation of Ni2P reduced adsorption capacity, affecting differently the micro- or mesoporous systems, depending on the zeolitic support. Ni2P deposition also modified the acidic properties of the zeolites due to the generation of new acid sites of moderate strength attributed to both Ni delta+ species (Lewis acid sites) and the presence of residual P - OH moieties (weak Bronsted acid sites).
The catalysts were tested in the HDO of guaiacol at 220 and 260 degrees C and 40 bar of H-2. In all cases, ZSM-5 based catalysts exhibited higher conversions and HDO efficiencies than Ni2P/MCM-22, which denotes that MFI zeolitic structure favors the deoxygenation of phenolic compounds, yielding cyclohexane as major reaction product.
This excellent catalytic performance is attributed to the combination of high surface area and optimal acidic properties since a synergetic effect was achieved between the acid sites of the raw zeolitic support and those provided by nickel phosphide having an enhanced accessibility. Thus, the best HDO performance was obtained over Ni2P supported on the pillared ZSM-5, showing a 78 % of guaiacol conversion and 95 % of selectivity towards deoxygenated molecules.